Purposeful setting of the bond properties and durability of ductile, strain-hardening composites based on recyclable polymer fibers and sustainable matrices

聚合物短纤维增强水泥基复合材料可获得高耐久性的应变硬化水泥基复合材料。实现这一点的先决条件是纤维-基质相互作用平衡良好，并且在整个使用寿命内具有稳定的界面性能。在以前的项目中已经证明，纤维的表面改性可以特别地影响与高水泥含量的混凝土基质的相互作用，从而影响复合材料的延展性。在目前申请的项目中，对这些相互作用的理解将通过系统地改变由可回收聚合物制成的纤维的表面性质并转移到新型、可持续的混凝土基质来加深。此外，还将包括对可持续小岛屿发展中国家长期行为的调查。该项目分为两个子项目。在第一个子项目中，高模聚合物纤维(PE、PP、PET)将通过不同物质的化学键和交联改性，以实现广泛的不同表面性质(非极性、酸性、碱性)，并提高纤维在碱性基质中的耐化学性。重点之一是分段改性，这应该能够使纤维末端在基质中牢固地锚固，并允许在裂缝桥接过程中中间部分的纤维脱粘。在第二个子项目中，改性纤维将被嵌入到可持续的混凝土基质中。根据LC³-Concept(石灰石煅烧粘土水泥)的概念，水泥熟料含量将减半，使用煅烧粘土和石灰石将排除飞灰和硅灰等工业副产品。纤维与基质的相互作用将通过单纤维拔出试验来量化，形成的纤维-基质界面相将从形态、物理和化学方面进行表征，以联系纤维和基质的性质。此外，还对纤维的破坏机理进行了分析。通过单轴拉伸试验研究了高韧性小体积混凝土的应力-应变行为。因此，将表征混合制度对纤维和颗粒分散以及纤维-基质-相互作用的影响。在不同环境下的长期暴露试验中，将弄清纤维改性对纤维增强复合材料耐久性的影响。基于这两个项目的结果，将发展一个经验材料模型和纤维-基质相互作用的目标设计的概念。

Strain-hardening cement-based composites (SHCC) with high durability can be achieved by reinforcement with short polymer fibers. Prerequisites for this are well-balanced fiber-matrix interactions and stable interphase properties over the entire service life. In the previous project it was proven that the interaction with concrete matrices of high cement content and, hence, the composite ductility can be specifically influenced by surface modification of the fibers. In the project presently applied for, the understanding of these interactions is to be deepened by the systematic variation of the surface properties of fibers made of recyclable polymers and transferred to novel, sustainable concrete matrices. In addition, investigations on the long-term behavior of the sustainable SHCC will be included.The project is subdivided into two subprojects. In the first subproject, high-modulus polymer fibers (PE, PP, PET) are to be modified by chemical bonding and cross-linking of different substances in order to achieve a wide range of different surface properties (non-polar, acidic, basic) and to improve the chemical resistance of the fibers in the alkaline matrices. One point of emphasis is to be sectional modification, which should enable strong anchoring of the fiber ends in the matrix and allow debonding of the fiber in the middle portion during the crack-bridging process.In the second subproject, the modified fibers will be embedded in sustainable concrete matrices. In accordance with the LC³-concept (Limestone Calcined Clay Cement), the cement clinker content will be halved and such industrial byproducts as fly ash and silica fume will be excluded by using calcined clay and limestone. The fiber-matrix interactions will be quantified by single-fiber pullout tests and the fiber-matrix interphases formed will be morphologically, then physically and chemically characterized to relate the properties of fiber and matrix. Furthermore, failure mechanisms of the fiber are to be analyzed. The stress-strain behavior of the highly ductile SHCC is to be investigated by means of uniaxial tension experiments. Thereby, the influences of the mixing regimes in respect of fiber and particle dispersions as well as fiber-matrix-interaction will be characterized. In long-term exposure tests subject to different environments, the influence of the fiber modifications on the durability of the fiber-reinforced composites will be clarified.Based on the results of both projects, an empirical material model and a concept for a targeted design of the fiber-matrix interaction of sustainable SHCC is to be developed.